Upload
finley
View
32
Download
0
Embed Size (px)
DESCRIPTION
Self-Consistent Simulations of the Interaction of Electron-Clouds and Beams with WARP-POSINST. Jean-Luc Vay Lawrence Berkeley National Laboratory Heavy Ion Fusion Science Virtual National Laboratory E-cloud 07, 9-12 April 2007, Daegu, Korea. Collaborators. - PowerPoint PPT Presentation
Citation preview
1Vay - Ecloud07
The Heavy Ion Fusion Science Virtual National Laboratory
Self-Consistent Simulations of the Interaction of Electron-Clouds and Beams
with WARP-POSINST
Jean-Luc Vay
Lawrence Berkeley National LaboratoryHeavy Ion Fusion Science Virtual National
Laboratory
E-cloud 07, 9-12 April 2007, Daegu, Korea
2Vay - Ecloud07
The Heavy Ion Fusion Science Virtual National Laboratory
Collaborators
M. A. Furman, C. M. Celata, P. A. Seidl, K. SonnadLawrence Berkeley National Laboratory
R. H. Cohen, A. Friedman, D. P. Grote, M. Kireeff Covo, A. W. Molvik
Lawrence Livermore National Laboratory
P. H. Stoltz, S. VeitzerTech-X Corporation
J. P. Verboncoeur University of California - Berkeley
3Vay - Ecloud07
The Heavy Ion Fusion Science Virtual National Laboratory
Our near term goal is High-Energy Density Physics (HEDP)...
Heavy Ion Inertial Fusion (HIF) goal is to develop an accelerator that can deliver beams to ignite an inertial fusion target
DT
Target requirements:
3-7 MJ x ~ 10 ns ~ 500 Terawatts
Ion Range: 0.02 - 0.2 g/cm2 1-10 GeV
dictate accelerator requirements:
A~200 ~1016 ions, 100 beams, 1-4 kA/beam
Artist view of a Heavy Ion Fusion driver
4Vay - Ecloud07
The Heavy Ion Fusion Science Virtual National Laboratory
We have a strong economic incentive to fill the pipe.
(from a WARP movie; see http://hif.lbl.gov/theory/simulation_movies.html)
Which elevates the probability of halo ions hitting structures.
5Vay - Ecloud07
The Heavy Ion Fusion Science Virtual National Laboratory
e-
i+haloe-
• ion induced emission from- expelled ions hitting vacuum wall- beam halo scraping
Sources of electron clouds
Primary:
Secondary:
i+ = ion e- = electrong = gas = photon
= instability
PositiveIon Beam
Pipe
e-
i+
g
g
• Ionization of - background gas - desorbed gas
• secondary emission from electron-wall collisions
e- e-e-
e-e-
• photo-emission from synchrotron radiation (HEP)
6Vay - Ecloud07
The Heavy Ion Fusion Science Virtual National Laboratory
Simulation goal - predictive capability
End-to-End 3-D self-consistent time-dependent simulations of beam, electrons and gas with self-field + external field (dipole, quadrupole, …).
Note: for Heavy Ion Fusion
accelerators studies,
self-consistent is a necessity!
WARP-3DT = 4.65s
200mA K+
Electrons
From source…
…to target.
HCX
7Vay - Ecloud07
The Heavy Ion Fusion Science Virtual National Laboratory
WARP is our main tool
3-D accelerator PIC code
• Geometry: 3D, (x,y), or (r,z)
• Field solvers: FFT, capacity matrix, multigrid
• Boundaries: “cut-cell” --- no restriction to “Legos”
• Bends: “warped” coordinates; no “reference orbit”
• Lattice: general; takes MAD input
-solenoids, dipoles, quads, sextupoles, …
-arbitrary fields, acceleration
• Diagnostics: Extensive snapshots and histories
• Parallel: MPI
• Python and Fortran: “steerable,” input decks are programs
8Vay - Ecloud07
The Heavy Ion Fusion Science Virtual National Laboratory
1
WARP-POSINST unique features
merge of WARP & POSINST
Key: operational; partially implemented (4/28/06)
+ new e-/gas modules
2
+ Adaptive Mesh Refinement
Z
R
concentrates resolution only where it is needed
3Speed-up x10-104
beam
quad
e- motion in a quad
+ Novel e- moverAllows large time step greater than cyclotron period with smooth transition from magnetized to non-magnetized regions
4 Speed-up x10-100
The Heavy Ion Fusion Science Virtual National Laboratory
Monte-Carlo generation of electrons with energy and angular dependence.Three components of emitted electrons:
backscattered:
rediffused:
true secondaries:
true sec.
back-scattered elastic
POSINST provides advanced SEY model.
re-diffused
I0
Its
Ie Ir
Phenomenological model:• based as much as possible on data for and d/dE• not unique (use simplest assumptions whenever data is not available)• many adjustable parameters, fixed by fitting and d/dE to data
10Vay - Ecloud07
The Heavy Ion Fusion Science Virtual National Laboratory
• ion-induced electron emission and cross-sections from the TxPhysics* module from Tech-X corporation (http://www.txcorp.com/technologies/TxPhysics),
• ion-induced neutral emission developed by J. Verboncoeur (UC-Berkeley).
We use third-party modules.
11Vay - Ecloud07
The Heavy Ion Fusion Science Virtual National Laboratory
(a) (b) (c)CapacitiveProbe (qf4)
Clearing electrodesSuppressor
Q1 Q2 Q3 Q4
K+ e-
Short experiment => need to deliberately amplify electron effects: let beam hit end-plate to generate copious electrons which propagate upstream.
End plate
INJECTOR
MATCHINGSECTION
ELECTROSTATICQUADRUPOLES
MAGNETICQUADRUPOLES
Benchmarked against dedicated experiment on HCX
Retarding Field Analyser (RFA)
Location of CurrentGas/Electron Experiments
GESD
1 MeV, 0.18 A, t ≈ 5 s, 6x1012 K+/pulse, 2 kV space charge, tune depression ≈ 0.1
12Vay - Ecloud07
The Heavy Ion Fusion Science Virtual National Laboratory
simulation
200mA K+ e-
0V 0V 0V V=-10kV, 0V
Suppressor offSuppressor on
experiment
Comparison sim/exp: clearing electrodes and e- supp. on/off
Time-dependent beam loading in WARP from moments history from HCX data:
• current
• energy• reconstructed distribution from XY, XX', YY' slit-plate measurements
(a) (b) (c)
Good semi quantitative agreement.measurement reconstruction
13Vay - Ecloud07
The Heavy Ion Fusion Science Virtual National Laboratory
1. Importance of secondaries - if secondary electron emission turned off:
2. run time ~3 days - without new electron mover and MR, run time would be ~1-2 months!
1. Importance of secondaries - if secondary electron emission turned off:
2. run time ~3 days - without new electron mover and MR, run time would be ~1-2 months!
Detailed exploration of dynamics of electrons in quadrupole
WARP-3DT = 4.65s
Oscillations
Beam ions hit end
plate
(a) (b) (c)
e-
0V 0V 0V/+9kV 0V
Q4Q3Q2Q1
200mA K+
200mA K+
Electrons
(c)0. 2. time (s) 6.
Simulation Experiment0.
-20.
-40.
I (m
A)
Potential contours
Simulation Experiment
(c)0. 2. time (s) 6.
I (m
A)
0.
-20.
-40.
Electrons bunching
~6 MHz signal in (C) in simulation AND experiment
WARP-3DT = 4.65s
14Vay - Ecloud07
The Heavy Ion Fusion Science Virtual National Laboratory
WARP/POSINST applied to High-Energy Physics
• LARP funding: simulation of e-cloud in LHC Proof of principle simulation:
• Fermilab: study of e-cloud in MI upgrade (K. Sonnad)• ILC: study of e-cloud in positron damping ring wigglers (C. Celata)
QuadrupolesDriftsBends
WARP/POSINST-3D - t = 300.5ns
AMR essentialX103-104 speed-up!
1 LHC FODO cell (~107m) - 5 bunches - periodic BC (04/06)
15Vay - Ecloud07
The Heavy Ion Fusion Science Virtual National Laboratory
“Quasi-static” mode added for codes comparisons.
A 2-D slab of electrons (macroparticles) is stepped backward (with small time steps) through the beam field and 2-D electron fields are stacked in a 3-D array, that is used to push the 3-D beam ions (with large time steps) using maps (as in HEADTAIL-CERN) or Leap-Frog (as in QUICKPIC-UCLA), allowing direct comparison.
2-D slab of electrons
3-D beam
benddrift driftquad
s
s0 lattice
16Vay - Ecloud07
The Heavy Ion Fusion Science Virtual National Laboratory
Time (ms)
Em
ittan
ces
X/Y
(-m
m-m
rad
)
2 stations/turn
Comparison WARP-QSM/HEADTAIL on CERN benchmark
Time (ms)
Em
ittan
ces
X/Y
(-m
m-m
rad
)
1 station/turn
WARP-QSM X,YHEADTAIL X,Y
WARP-QSM X,YHEADTAIL X,Y
Note: WARP-QSM now parallel
17Vay - Ecloud07
The Heavy Ion Fusion Science Virtual National Laboratory
How can FSC compete with QS? Recent key observation: range of space and time scales is not a Lorentz invariant*
• same event (two objects crossing) in two frames
Consequences• there exists an optimum frame which minimizes ranges,• for first-principle simulations (PIC), costT/t ~ 2 (L/l*T/t ~ 4 w/o moving window),
*J.-L. Vay, PRL 98, 130405 (2007) for large , potential savings are HUGE!for large , potential savings are HUGE!
= (L/l, T/t)
0
0
0
0
0
Range of space/time scales =(L/l,T/t) vary
continuously as 2
spac
esp
ace+
time
F0-center of mass frame FB-rest frame of “B”
x
y
x
y
18Vay - Ecloud07
The Heavy Ion Fusion Science Virtual National Laboratory
Free electron lasersHEP accelerators (e-cloud)
1nm10km
10m
10cm
Laser-plasma acceleration
x10003c
m
1m
In laboratory frame.longitudinal scale x1000/x1000000…
… so-called “multiscale” problems = very challenging to model!
Use of approximations (quasi-static, eikonal, …).
A few systems of interest which might benefit
x1000000x1000
10km/10cm=100,000. 10m/1nm=10,000,000,000.
3cm/1m=30,000.
19Vay - Ecloud07
The Heavy Ion Fusion Science Virtual National Laboratory
10km
10cm
10km/10cm=100,000.
compaction
x103
450m
4.5m
frame ≈22
450m/4.5m=100.
10m
10m/1nm=10,000,000,000.
1nm1nm
compaction
x3.107
2.5m
m
4m
2.5mm/4m=625.
frame ≈4000
3cm
1m
3cm/1m=30,000.
compaction
x560
1.6m
m
30m
1.6mm/30m=53.
frame ≈19
Hendrik Lorentz
Lorentz transformation => large level of compaction of scales
HEP accelerators (e-cloud)
Laser-plasma acceleration
Free electron lasers
Note: of interest only if modeling beam and e-cloud, i.e. for self-consistent calculations.
20Vay - Ecloud07
The Heavy Ion Fusion Science Virtual National Laboratory
Boosted frame calculation sampleproton bunch through a given e– cloud
This is a proof-of-principle computation:hose instability of a proton bunch
Proton energy: =500 in Lab• L= 5 km, continuous focusing
electron streamlinesbeam
proton bunch radius vs. zCPU time:
• lab frame: >2 weeks• frame with 2=512: <30 min
CPU time:• lab frame: >2 weeks• frame with 2=512: <30 min
Speedup x1000
21Vay - Ecloud07
The Heavy Ion Fusion Science Virtual National Laboratory
Summary
• WARP/POSINST code suite developed for HIF e-cloud studies– Parallel 3-D AMR-PlC code with accelerator lattice follows beam self-
consistently with gas/electrons generation and evolution,
• Benchmarked against HCX– highly instrumented section dedicated to e-cloud studies,
• Being applied outside HIF/HEDP, to HEP accelerators– Implemented “quasi-static” mode for direct comparison to
HEADTAIL/QUICKPIC,
– fund that cost of self-consistent calculation is greatly reduced in Lorentz boosted frame (with >>1), thanks to relativistic contraction/dilatation bridging space/time scales disparities,
– 1000x speedup demonstrated on proof-of-principle case,
– will apply to LHC, Fermilab MI, ILC,
– assess 3-D effects, gain/complications of calculation in boosted frame.